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skg16.3 > Compressor - Firdaus Sabturani > Flashcards

Compressor - Firdaus Sabturani Flashcards

1
Q

Compressor

A

a mechanical device that increases the pressure
of compressible fluid e.g. natural gas, air, etc

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2
Q

Compressors are similar to pumps

A

both increase the pressure on a fluid and both can transport the fluid through a pipe.

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3
Q

Reciprocating Compressor Types

A
  • Horizontal : Traditional / Free floating
  • Vertical : Traditional / Labyrinth Ring
  • High Speed : Traditional
  • Integral with Engine
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4
Q

Reciprocating Compressor Capacity Control

A
  • Variable speed control
  • Unloader control
  • Suction throttling
  • Recirculation bypass
  • On-off control
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5
Q

Centrifugal Compressor Types

A
  • Single / Multi stage
  • Between bearings / Overhung
  • Inter cooled
  • Side Load
  • Horizontal / Vertical split / Barrel
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6
Q

Axial Compressor

A
  • Gas flows in direction of rotating shaft
  • Can be built for lower pressures only (0.7 to 6.8 Bar)
  • High flow rate & Efficiency
  • Not as common as centrifugal compressors
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7
Q

Performance Control by Blow-off or Recycle

A
  • Most inefficient control method
  • Regularly found inplant air systems
  • Rare in other systems
  • Not recommended
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8
Q

Compressor Capacity Control Can be based on controlling:

A

– Net flow to the user ( recycle )
– Discharge pressure
– Suction pressure
– Variable Inlet Guide Vanes
– Speed

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9
Q

Performance Control by Discharge Throttling

A
  • Extremely inefficient
    (approx. the same power for every load)
  • Rarely used
  • Not recommended
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10
Q

Performance Control by Suction Throttling

A
  • Common on electric motor machines
  • Much more efficient than discharge throttling
  • Power consumed proportional to the load
  • Throttle losses are across suction valve
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11
Q

Performance Control by Adjustable Guide vanes

A
  • Improved turndown
  • More efficient than suction throttling
  • Power consumed is proportional to the load
  • Power loss on inlet throttling is eliminated
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12
Q

Performance Control by Speed Variation

A
  • Most efficient (Power  f(N)3
    )
  • Steam turbine, gas turbine or
    variable speed electric motor
  • Typically capital investment higher
    than with other systems
  • No throttle losses
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13
Q

Surge Phenomena

A

– A break down of flow through the compressor
– Surge occurs when the machine tries to compress a gas to too high pressure at too low
flow

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14
Q

Surge symptoms

A

– Flow fluctuations and oscillations
– Temperature rise
– Compressor vibration
– Noise !

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15
Q

Process parameters during surge

FLOW

A
  • Rapid flow oscillations
  • Thrust reversals
  • Potential damage
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16
Q

Process parameters during surge

PRESSURE

A
  • Rapid pressure oscillations
    with process instability
17
Q

Process parameters during surge

TEMPERATURE

A
  • Rising temperatures inside
    compressor
18
Q

Consequences of Surge

A
  • Process instability
  • Compressor sequentially starting with damage to seals followed by
    damage to bearings, impellers and shaft with increase in severity of the
    surge
  • Increased seal clearances and leakage
  • Reduced compressor life
  • Catastrophic damage leading to prolong production loss
19
Q

Factors leading to onset of surge

A
  • Non-compliance to procedures during start-up & shutdown
  • Operation at high throughput during normal operation with the following
    scenarios:
  • Trips - Power loss
  • Operator errors - Process upsets
  • Load changes - Gas composition changes
  • Cooler problems - Filter or strainer problems
  • Driver problems
20
Q

Basic Anti-surge Control System

A
  • The anti-surge controller UIC-1 protects the compressor against surge
    by opening the recycle valve
  • Opening of the recycle valve lowers the resistance felt by the
    compressor
  • This takes the compressor away from surge
21
Q

Surge line moves closer to operating point if :

A
  • Molecular weight of gas reduces
  • Suction temperature increases
  • Suction pressure reduces
  • Impellers become fouled
22
Q

Effects of Fouling:

A
  • Deposits
  • Polymerisation
  • Performance loss
23
Q

Prevention of Fouling:

A
  • Process parameters
  • Anti-fouling coatings ( Sermalon )
  • Liquid Injection
    – Pipe
    – Compressor inlet
  • Off-line washing

skg16.3 (12 decks)

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